Means of charging dust at wire supports of electrical precipitators



Nov. 12, 1940. w PENNEY I ,7 2,221, 03

MEANS OF CHARGING DUST AT WIRE SUPPORTS OF ELECTRICAL PRECIPITATORSFiled Oct. 20, 1939 WITNESSES: I INVENTOR C? Gqy/ardh/Qnflef.

V ATTORNEY Patented Nov. 12, 1940 UNITED STATES PATENT OFFICE M'EAN S FCHARGING DUST AT WIRE SUP- PORTS OF ELECTRICAL PRECIPITATORSPennsylvania Application October 20, 1939, Serial No. 300,392 7 Claims.(c1. 183-7) My invention relates to electrical precipitators employed toelectrically precipitate from air, or any othergaseous medium, anycontained, or suspended, dust particles, fogs, smokes, or

other particulate matter, and which for con-' venience, is hereinafterembracively termed dust. The present invention is related somewhat tothe gas-purifying electrical precipitator comprising thesubject matterof my Patent No. 2,129,783, 10 issued September 13, 1938, and assignedto'the Westinghouse Electric & Manufacturing Company. In such aprecipitator, thegas is first' blown through an ionizing zone or chamberand then through a precipitating zone or chamber,

a significant feature of theprecipitator being that the ionizing wire orwires are of such small diameter that practically utilizable charging ofthe suspended particles of dust may be obtained at a wire-chargingvoltage giving ionizing ourrents at which negligible ozone generationoccurs,

and that the power input is'low when the precipitator is used forcleaning air.

The ionizing wire of such a precipitator is preferably less than 32mils-in diameter. In the usual construction of a precipitator built inaccordance with the teachings and principles contained in the aforesaidPenney patent, the wire is much finer than this upper limit and isfrequently as little as 5 mils in diameter or even 130 less, the actualdiameter being kept as small as possible, consistent with sufficientstrength to withstand rough usage in the actual commercial embodimentsof the apparatus. In general, theionizing wire of such a precipitator isusually 35 maintained taut, or in some degree of tension. The ionizingwire itself is part of an ionizing means which usually comprises one ormore such ionizing wires alternating with curved electrodes, generallygrounded, and designated as ground electrodes, at a suitable potentialwith respect to the wires for creating an ionized electrostatic fieldextending in the regions between the wires and ground electrodes and oflow power consumption and negligible generation of ozone or oxides ofnitrogen.

Since the ionizing wires are at a high potential relative to the groundelectrodes, thewires must necessarily be'insulated from the electrodes;and, moreover, since a supporting structure rfiust be provided fortheionizing means, the ground electrodes are generally part of, orelectricallyconnected to, the supporting structure which may be in theform of a metal casing. This means that the ionizing wires must also beelectrically insulated'from this casing, and for this the precipitatingchamber.

purpose, the parts of the wire in proximity to the casing sides aresecured between end supports spaced and insulated from the proximatesides of the casing, or box, or whatever form the supporting means maytake or be called. This space between the wire end supports, or the endof a wire, and the casing sides is a region in which, in priorstructures, the ionizing current is inadequate, that is, the dustcarried by theair or gas passsing through the region 1 is notsufliciently electrically-charged for efllcient precipitation of thedust subsequently in This regionof in-'- adequate ionization is enlargedright at the end supports for the wires which introduce dark or shieldedspots, extending about or so from the support, of little or inadequateionization.- Dark spots are also present to some. extent at anyintermediate supports for the ionizing wires,

which are generally employed in the longer ioniz- 20 ing units.

In large precipitating apparatus having long ionizing wires, transverseto the gas flow, the

total regions of inadequate, or less-than sufficient, ionization issmall compared to the total 25 regions of adequate, or sufficient,ionization to charge the dust particles for precipitation, and thetotaloverall cleaning efiiciency of the apparatus is little afiected bythe dark regions. But as thelength oi the wires goes down, theproportion of the former regions to the latter in-' creases with amanifest adverse afiect on efliciency. Thus, for example, in anapparatus in which nine tenths of the air is sufficiently well ionizedto yield a cleaning efficiency of 95%, and the remaining one-tenth isinadequately ionized so that its cleaning efliciency is, only, say 50%,then the total efliciency would be only 90.5%. When even 90.5%efliciency represents a high degree of air cleaning possible only withelec- 40 trical preeipitators of the type described and. ample forpractically all cleaning purposes, neverthelesa'itnis an object of thisinvention to devise a means to further increase the efficiency ofprecipitating apparatus by increasing the ion- 45 ization in the regionspreviously inadequately ionized. X I

It is an object of y invention, therefore,

to provide a means for assuring adequate ionization of all the airor gaspassing through an electrical preeipitator of the type described, and

izing-wire supports.

the means also acting as bafiles or air-guides preventing the air fromflowing into these end spaces or dark spots without first passingthrough the adequately ionized fields thus created. I

With the foregoing and other objects in view, my invention consists ofthe features, elements, combination and apparatus hereinafter describedand claimed, and illustrated in the accompanying drawing, in which:

Figure 1 is a longitudinal, vertical, sectional view of an exemplaryform of embodiment of my invention, the section plane being indicated inI-I of Fig. 2;

Fig. 2 is a vertical, sectional view at right angles to the view of Fig.1 on a plane indicated by the line II-II of Fig. 1 andwith parts brokenaway or omitted for purposes of clarity of illustration;

Figs. 3 and 4 are fragmentary sectional views of details and taken onthe lines III-III of Fig. l and IV-IV of Fig. 2, respectively, Fig. 4showing a slight modification;

Fig. 5 is a cross-sectional view through another embodiment of aprecipitator ionizing unit such as described and claimed in theapplication of Edward H. R. Pegg, Serial No. 286,577, filed July 26,1939, and assigned to the Westinghouse Electric & Manufacturing Company;and

Fig. 6 is a cross-sectional view of a detail showing baiile meansconnected to a cell side rather than to the central ground electrode ofFig. 5.

In the illustrated embodiments of my invention, which are only a few ofthe many forms which the invention can take, air to be treated orcleaned is drawn through the top of a precipitator cabinet or casing Ithrough a protective screening 2 and passes downwardly to an ionizingunit or chamber 3 in the top of the casing, where the air andparticulate matter it contains are ionized or charged, after which theair continues downwardly and passes into a precipitating chamber 4 wherethe dust may be precipitated or agglomerated, after which the air maycontinue for further treatment, if desired or may be discharged into thepremises, a blower 5 being illustrative as means for drawing or forcingthe air through the apparatus.

The ionizing chamber or zone 3 usually comprises a plurality of ionizingmeans disposed transversely with respect to the direction of airflow,each ionizing means comprising a fine wire 6 which is disposed incentrally-spaced relation between two relatively large electrodes 1which are preferably tubular or curved in section so that they presentcurved surfaces toward the ionizing wire.

The tubular electrodes 1 are, in this embodiment, directly secured to,and, therefore, grounded on the-precipitator casing I, and the ionizingwires 6 are suspended between rigid metal-end supports 8 carried by askeleton framework 9 which is supported inside the casing by insulatorsH. For the longer wires, it is usually necessary to support each wire atone or more intermediate points, as by means of rigid metal intermediatesupports 1 2 which are also carried I and spaced closely togetherparallel to the direc* tion of air flow. The insulated precipitatingplates 20 are supported and spaced by notched metallic supporting bars22 carried by insulating means including the insulators 23 so that theprecipitating plates and the metallic supporting bars arecompletelyinsulated from-the grounded plates and precipitator casing.The non-insulated grounded precipitating plates 2| are supported andspaced by means of notched bars 24 carried by the casing I.

As explained in my aforesaid patent the ionizing wires 6 and theinsulated precipitator plates 20 are, preferably, unidirectionallycharged with respect to the uninsulated or grounded parts which comprisethe ground electrodes 1 and the grounded plates 2|. Because of thegreater spacing between each wire 6 and its associated tubularelectrodes 1 as comparedwith the spacing between the alternate plates 20and 2| of the precipitating chamber, the ionizing voltage, that is, thevoltage between an ionizing wire and ground electrode 1, is frequentlyhigher than the precipitating voltage, that is, the voltage between theplates 20 and 2|. I have indicated that unidirectional voltagesareapplied to the ionizing wire 6 and the precipitating plates 20 byschematically showing, as indicated by the reference numerals 25 and 26,respectively, the positive terminal of the unidirectional ionizingsource of voltage 1+ and the positive terminal of the unidirectionalprecipitating source of voltage P+. The negative terminal or terminalsof the voltage means is represented schematically as grounded on theframe of the casing l, as indicated at 30, it being understood thatbecause the metal bars 24 are secured to the casing, the grounded plates2| are therefore also conductively connected to the negative terminals,as are the ground electrodes 1.

The structure thus described has been found satisfactory in use, butnevertheless, its efliciency can be impaired by dark regions ofinadequate ionization for it may be observed that, if no other meanswere supplied, air could fiow in the end spaces 3| between the endsupports 8 and opwires and may extend approximately /2" or so from theactual point of contact between the wires and the supports, These darkspots or shielded regions which have been found to exist are moreparticularly pointed outin the application of Russell A. Nielsen, SerialNo. 286,589, filed July 26, 1939, and assigned to the WestinghouseElectric & Manufacturing Company.

In order to completely accomplish the purpose of my invention, I provideend baflle's and electrode means 33 for directing the air that mightotherwise flow along the inside of the casing sides 32, in a directionwhich will make it pass through anadequately ionized region, and forthesame purpose, I also provide intermediate air baflie and electrodemeans 34 to force the air mediate supports l2 in the vicinity oftheionizing I cylindrical and extends between two of the adthereto.

jacent ground electrodes 1 contacting them so that it is in electricallyconductive relation The curvature of these bafiles' is such that theradius is approximately the same as the distance from a wire to eitherof the ground electrodes I. In actual practice I prefer to make thebafiles or shield as far or slightly further from the ionizing wire asare the ground electrodes I.

In extent, the end baflle '33 covers the end space 3|. and protrudesslightlyinward of the end support 8 for a distance sufiicient to create,in conjunction with the ionizing wire, a substantially vertical ionizedfield. The intermediate bafiies 34 are similarly disposed .with partsprotruding parallel to the ionizing wire and for extents a little beyondthe intermediate supports. If desired, the free edges of the baffles maybe curled, as shown in Fig. 4, to decrease air resistance and preventcorona formation from sharp edges.

Referring back to Fig. 3, it may be observed that since the bafiies areat ground potential, an electrostatic field will be created between thebafiles and the ionizing wire, as shown more or less symbolically by thesomewhat radial lines extending from the wire 6 in Fig. 3, and thedotted lines to the, bafiies from the wire in Fig. 4.

This ionizing field has approximately the same gradient as a fielddirected to the ground electrodes since the metallic baflles 33 and 36are disposed approximately as far, from the ionizing wire as the groundelectrodes. I prefer to avoid a shorter spacing between the shields andthe ionizing wires. because of the possibility that the increased fieldgradient might yield increased ozone generation or, if short enough,might possibly breakdown the air space completely at times. I prefer toavoid too great a spacing between the points of the shields and the wirefor the reason that the field might become too weak for an adequateionizing current so that the air-borne dust will not be adequatelycharged.

It is always desirable to make the baflles as narrow as possible inorder to reduce the re- I sistance to air flow. Since the field from theionizing wire to the bafiles can be angular with respect to a verticalplane, the bafiles need not necessarily extend beyond the dark spots onthe wire, and may, in fact, be of less length. For example, I have foundthat an intermediate bafile of width created a field of adequateionization.

In operation, the air-flow entering the top of the casing, which isshown by the arrows, may be deemed to be divided into distinct portions:that part, which flows straight through, and that part which flows downaround the baflles or shields 33 and 34 and into thespace 3! at thesides of the casing or into the dark regions near the intermediatesupports l2. The first portion will, of course, be adequately ionized byvirtue of its passing directly between a freely-suspended part of thewire 6 and a part of the grounded electrode 1, while the second portionwill be ionized now by the field existing between the wire 6 and thebaflles 33 and 34, the air, necessarily being compelled to pass throughthis field, as shown by the arrows and 36, these arrows beingrepresentative of the gas flowing to compel the gas to flow throughadequately ionized regions in its entirety. There are no dark spots orend spaces through which the air may flow without being ionized, and Ihave thus improved an electrical precipitator of the typedescribed tothat extent. 7

In Fig. 5 I show the application of my invention to a more modern typeof ionizing unit, as more particularly described in the aforesaid Peggapplication Serial No. 286,572.- Such a unit generally comprises acentral electrode 40 upon which is secured an end of each of a pluralityof spaced insulators 42, across the other ends of which extends a bar 44to which the end supports 46 for ionizing wires 48 and 50 may besecured. The casing I in this embodiment takesthe formof a rectangularcell having sides 52 parallel to the ionizing wires, and provided withturned-over and rounded edges toprovide ground electrodes 54 cooperatingwith the other ground electrode 40.

The ground electrode 40, the insulator 42. the bar 44, the end supports46, and the wires 48 and 50 are assembled as a unit'in themselves andcan be secured to the casing, as more particularly described in thementioned Pe g application. To add a baffle structure to this.

unit, a suitably curved shield 56 is provided having a central portion58 fitting the lower part of the tubular electrode 4|! and an aperturethrough which the bolt 60. passes which secures an insulator 42 to theelectrode 40. Curved shield and electrode portions 62 extend from bothsides of the central portion 58, each terminating in curved end portions64 fitting the contour of the ground electrodes 54, the curved portions62 of shields 56 having just enough spring in them so as to pressagainst these electrodes.

In the event it is desired to secure the shields to the casing groundelectrodes rather than to the removable ionizingunit, it is possible tosecure, as by welding, a side of a shield 66 to the electrodes 54, theother side being provided with a down-turned edge 68 to make acontactwith the tubular electrode 40 when the ionizing unit, as a whole, isinserted in its place in the cell I.

It is, of course, to be understood that the different baflles 33 and 34,56 and 66, suitably contact the ground electrodes, and are suitablysecured, as by soldering or welding orsom other means, to one or more ofthem to maintain them in place. It is important, however, to note thatthe end bafiles preferably divert the air flow so that none of it canpass directly along the sides ofthe casing or cell, but must' passthrough the ionized field between the end bafiie and that part about theionizing wire li'beyond the dark spot at its support, and, in the sameway, the intermediate baffles deflect the air flow so that move: ment ofthe air through the dark spots thereat is preceded by flow through theadequately ion ized field between the end portions of the shield and thewire 6; 1 While I have shown and described my invention in accordance inthe preferred forms of embodiments, and have suggested certainoperations and conditions in accordance with my best understanding ofthe same at the present time, I desire it to be distinctly understoodthat I am not altogether limited to these understandings or conditionsor to the particular forms shown inthe drawing.

I claim as my invention:

1. A device of the class described comprising a gas-cleaningprecipitator having an ionizing chamber and a separate precipitatingchamber successively in. the path of a gas-flow for the cleaning ofparticulate matter-from the gas'said' ionizing chamber being providedwith one or more ionizing units, each unit being disposed transverse tothe gas-flow and comprising an insulatedly supported ionizing wirespaced between substantially uninsulated relatively large groundelectrodes, a plurality of relatively rigid supporting means includingwire supporting members for I insulatedly supporting said wire, andadditional limited-extent ground electrode means substantially spanningsaid large'electrodes for-serving as an adjunct to said relatively largeelectrodes and cooperating with said wire for creating an ionized fieldthrough which the portion of said gas-flow in the vicinity of saidmembers must 2. The structure of claim 1 characteribed by the last saidmeans comprising curved metallic sheets contacting said groundelectrodes and spaced on the side of .said wire or wires opposite thesaid members. r

3. The structure of claim 1 characterized by the last said meanscomprising curved metallic sheets contacting said ground electrodes andspaced on the side of said wire opposite said members, and of an extentslightly beyond said I members in the direction of the wire, thecurvature of said sheets being such that the inner surfaces aresubstantially the same distance, or a slightly greater distance,awayfrom the said ionizing wire as are the said large ground electrodes.e I

4. An electrical precipitator cell having as a part thereof: a metalliccasing having sides; and as anadditional part a substantially straighttubular electrode, a plurality of insulators, means for supporting anend of each of said insulators on said electrode intermediate the endsthereof, a plurality of armed brackets, means for securing said bracketsto the other ends of said insulators with their arms in spaced relationto said electrode, ionizer means including an ionizing wire secured tocertain of said arms in spaced relation to said electrode, andparallelingsaid electrode; and a parti-cylindrical curved metallic sheetcontacting said electrode, disposed on the side opposite said bracketsand bafiing the spaces between the casing sides of said wire and saidbrackets and extending sli htly inward beyond the nearest end of said.ionizing wire. p

5. A device of the class described having an ionizing zone and aprecipitating zone successively in the path of a gas-flow for thecleaning of particulate matter ircm the gas, said precipitating zonedefining the pathot the gas-flow.

thereat, an open metallic casing having opposed sides between.- whichthe gas flows, an ionizing wire inside said casing transverse to thegas-flow, means on one side of said wire for supporting said-wire ininsulated relation to said casing so ,that it extends almost to saidsides but leaves spaces therewith through which gas might flow, without4 being adequately ionized, and curved grounded electrode means spacedfrom said wire on the side of said wire away from said supporting means,cooperating with said ionizing wire for creating an'adequately ionizedfield in the path of the portion oi gases flowing through said spaces.

6. In adevice-o! the class described having an ionizing zone and aprecipitating zone successively in the path of a gas-flow tor thecleaning of particulate matter from the gas, ionizing means comprisingan ionizing wire and a parallel ground electrode, means disposed on oneside of said wire for supporting said wire in insulated spaced relationto said electrode, and means disposed on the other side of said wire forcreating an adequately ionized field with the parts of the wire inproximity to said supportirig means, and to guide the portion of saidgas flow about said supporting means through'said field.

ionizing wire spaced from one pair of said opposed sides, spaced groundelectrodes paralleling said wire to provide an ionizing field with saidwire and means including arms for insulatedly supporting saidwire'between said ground electrodes, said wire being of less than 32mils in diameter and being of such fineness that ade quatc charging ofsuspended particles in the gas is obtained at a wire-charging voltagebelow the critical corona. voltages, and yielding ionizing currents ofnegligible zone generation; and additional ground electrode .means.spaced from 5 said wire for providing, with said wire, anionizing fieldin the path of the gas-flow at said arms, the last said field merginginto the first said field.

' GAYLORD W.- PENNEY.

